It is well known that, the solid Ti catalyst component comprising magnesium, titanium, halogen, and electron donor as basic ingredients can be used in the polymerization of olefins, and especially used in the polymerization of alpha olefins having three or more carbon atoms for obtaining polymers with a higher stereoregularity in a higher yield. Electron donor compound is one of the essential ingredients of the catalyst component. With the development of the internal electron donor compound, new catalysts for polyolefin are developed constantly. At present, a large amount of electron donor compounds have been disclosed, for instance, polycarboxylic acid, monocarboxylic ester or polycarboxylic ester, anhydride, ketone, monoether or polyether, alcohol, amine and derivatives thereof.
A kind of 1,3-diol diester compound is disclosed in CN1453298A and CN1580034A. A catalyst with excellent comprehensive properties can be obtained by using said 1,3-diol diester compound as electron donor in the catalyst for olefin polymerization,. When the catalyst is used for propylene polymerization, higher polymerization activity and higher stereospecificity can be obtained, and the molecular weight distribution of the obtained polymer is wide as well. However, the acitivity and stereospecificity of the catalyst are not satisfactory. And especially in the production of polymers with high melt index, the isotactic index of the obtained polymers is not high enough, and thus an further improvement is needed.
As to the 1,3-diol diester compound disclosed, when the four groups connected to one carbon atom are different from each other, there are two spatial connection modes for the four groups connected to the carbon atom. The two connection modes are mirror images of each other, as left hand and right hand, and can not be completely superimposed onto each other. This kind of compound is known as “chiral compound”. The inventor surprisingly finds that, if the diol diester compounds as shown in Formula (I) with several conformational isomers are used as internal electron donor to prepare the catalyst, the activity and stereospecificity of the catalyst would be satisfactory only when the catalyst contains a certain amount of isomer with Fischer projection formula as shown in Formula (II). And especially in the production of polymers with high melt index, the isotactic index of the obtained polymers is increased substantially.